Patent application title: Method for setting the air ratio on a firing device and a firing device

Abstract:

The temperature generated by a firing apparatus, particularly a gas
burner, depends on the mixing ratio between the quantity of air and the
quantity of gas fed to the firing apparatus, characterized by the excess
air coefficient λ, at a predefined burner load (air mass flow rate)
in such a way that the temperature generated by the firing apparatus
reaches a maximum when λ=1. According to the inventive method for
adjusting the excess air coefficient, said maximum temperature Tmax
is determined, whereupon the desired setpoint value λhy of the
excess air coefficient is adjusted and the associated setpoint
temperature Tsoll, is measured. A characteristic curve which
represents the correlation between the respective air mass flow rates and
the setpoint temperatures at the setpoint value λhy of the
excess air coefficient and allows combustion to be regulated to an
optimal hygienic state can be determined from said determined correlation
between the setpoint temperatures Tsoll at different predefined
burner loads. The inventive firing apparatus is adapted to carry out said
method and especially comprises a mass flow sensor in the air delivery
zone as well as a temperature sensor in the effective range of the burner
flame.

Claims:

1. A method for setting operating parameters on a firing device, in
particular on a gas burner with a fan, the temperature produced by the
firing device being dependent upon the value of the air ratio and having
a maximum at the value λ1=1, comprising the steps:controlling
a pre-determined air mass flow;establishing the gas mass flow
corresponding to the temperature (Tmax);defining a desired value for
the air ratio for a desired hygienic combustion;controlling the desired
hygienic combustion by increasing the air mass flow by the factor with a
constant supply of gas mass flow.

2. The method according to claim 1, wherein the air mass flow
corresponding to the hygienic desired value for the air ratio is
controlled by changing the ventilator speed of the fan.

3. The method according to claim 1, wherein the air mass flow and/or the
gas mass flow are measured respectively by a mass flow sensor.

4. The method according to any of the preceding claims claim 1, wherein
the gas mass flow corresponding to the temperature maximum is established
by iterative approximation of the value of the gas mass flow to the value
corresponding to the temperature maximum.

5. The method according to claim 1, wherein the desired value for the air
ratio is approximately 1.3.

6. A firing device, in particular a gas burner according to claim 1,
wherein the firing device is adapted to implement a method according to
claim 1.

7. The firing device according to claim 6, wherein the firing device has a
temperature sensor in the effective region of the burner flame of the
firing device.

8. The firing device according to claim 6, wherein the firing device has a
valve with a correcting element for setting the gas mass flow, in
particular with a stepper motor, a pulse width modulated coil or a coil
controlled by an electrical value.

9. The firing device according to claim 6, wherein the firing device has
at least one mass flow sensor and/or volume flow sensor for measuring the
quantity of air supplied to the firing device per unit of time and/or the
quantity of gas supplied per unit of time and/or the quantity of mixture
of air and gas supplied.

10. The method according to claim 2, wherein the air mass flow and/or the
gas mass flow are measured respectively by a mass flow sensor.

11. The method according to claim 2, wherein the gas mass flow
corresponding to the temperature maximum is established by iterative
approximation of the value of the gas mass flow to the value
corresponding to the temperature maximum.

12. The method according to claim 3, wherein the gas mass flow
corresponding to the temperature maximum is established by iterative
approximation of the value of the gas mass flow to the value
corresponding to the temperature maximum.

13. The method according to claim 2 wherein the desired value for the air
ratio is approximately 1.3.

14. The method according to claim 3 wherein the desired value for the air
ratio is approximately 1.3.

15. The method according to claim 4 wherein the desired value for the air
ratio is approximately 1.3.

16. The firing device according to claim 7, wherein the firing device has
a valve with a correcting element for setting the gas mass flow, in
particular with a stepper motor, a pulse width modulated coil or a coil
controlled by an electrical value.

17. The firing device according to claim 7, wherein the firing device has
at least one mass flow sensor and/or volume flow sensor for measuring the
quantity of air supplied to the firing device per unit of time and/or the
quantity of gas supplied per unit of time and/or the quantity of mixture
of air and gas supplied.

18. The firing device according to claim 8, wherein the firing device has
at least one mass flow sensor and/or volume flow sensor for measuring the
quantity of air supplied to the firing device per unit of time and/or the
quantity of gas supplied per unit of time and/or the quantity of mixture
of air and gas supplied.

Description:

[0001]A method for setting operating parameters on a firing device, in
particular on a gas burner with a fan, the temperature (Tactual)
produced by the firing device being dependent upon the value of the air
ratio (A) and having a maximum (Tmax) at the value λ1=1.
Moreover, the invention relates to a firing device, in particular a gas
burner, which is adapted to implement the method.

[0002]In households, gas burners are used, for example as continuous-flow
heaters, for preparing hot water in a boiler, or for providing heating
heat. In the respective operating states, different requirements are made
of the equipment. This relates in particular to the power output of the
burner, generally called the burner load, and the temperature produced by
the burner flame.

[0003]The burner load is substantially determined by the setting of the
quantity of combustion air and of the mix ratio between gas and air. The
mix ratio is set, in particular with gas burners used in households, by
means of a pneumatic gas regulation valve (principle of the pneumatic
combination). With the pneumatic regulation, pressures or pressure
differences are measured at restricting orifices, in narrowings or in
venturi nozzles. These values are used as control values for the gas
regulation valve. However, a disadvantage of pneumatic regulation is in
particular that sensitive mechanical components have to be used which are
associated with hysteresis effects due to friction. In particular with
low working pressures, inaccuracies therefore occur. Moreover, the cost
of producing the pneumatic gas regulation valves equipped with membranes
is considerable due to the high requirements for precision. Moreover, in
the pneumatic combination, changes to the gas type and quality can not be
reacted to flexibly. In order to be able to make, nevertheless, the
required adaptations of the gas supply, additional devices, e.g. nozzles
and restricting orifices, must be provided dependent upon the gas type,
but this means additional expense.

[0004]With electronic control, however, a simply controllable gas
regulation valve, possibly with a pulse width modulated coil or stepper
motor, can be used in order to set the desired quantity of air and the
desired gas/air mix ratio in association with a fan with a controllable
speed (electronic combination). In this way it is possible to react
flexibly to changes in the gas quality.

[0005]With a pre-determined quantity of air, the mix ratio between gas and
air is to be set such that the gas combusts as completely and cleanly as
possible. In order to characterise the mix ratio between gas and air the
air ratio λ is typically used. This is defined as the ratio of the
actually supplied quantity of air to the quantity of air theoretically
required for optimal stoichiometric combustion. In order to optimise the
exhaust gas values (CO, CO2), gas burners are typically operated
with an excess of air. The desired value for the air ratio λs
for hygienically optimal combustion is 1.3. When operating a gas burner
with an electronic combination, it must be ensured that with the
different burner loads the air ratio A is always as close as possible to
the desired value λs. In addition, it should be noted that the
operating conditions can change after the equipment has started up, and
then the parameters of the combustion regulation must be correspondingly
adapted.

[0006]In EP 770 824 B1 a method is described in which, with the help of an
ionisation electrode a calibration cycle is run through in order to
adjust the electric desired value of the ionisation electrode. In this
way, changes to the thermal coupling between the ionisation electrode and
the gas burner which arise, for example, due to wear and tear, bending
and due to contamination, are equalised.

[0007]With this method, which only falls back on the signal from the
ionisation electrode, it is possible to exactly determine the ionisation
signal for λ=1. However, the desired value for the air ratio can
then not be set precisely because, for example, the characteristic line
of the equipment is not taken into consideration.

[0008]It is therefore the object of the invention to specify a method with
which the parameters for the combustion can be set, simply and reliably,
on required burner loads. It is also the object of the invention to
provide an appropriate apparatus with which the method can be
implemented.

[0009]The object is fulfilled by a method according to the main claim and
by an apparatus according to claim 6.

[0010]In the method for setting operating parameters on a firing device,
in particular on a gas burner with a fan, the temperature (Tactual)
produced by the firing device being dependent upon the value of the air
ratio (A) and having a maximum (Tmax) at the value λ1=1,
the following steps are implemented: [0011]controlling a pre-determined
air mass flow (mL); [0012]establishing the gas mass flow
(m.sub.GTmax) corresponding to the temperature (Tmax);
[0013]defining a desired value for the air ratio (λhy) for a
desired hygienic combustion; [0014]controlling the desired hygienic
combustion by increasing the air mass flow (mL) by the factor
(λhy) with a constant supply of gas mass flow (m.sub.GTmax).

[0015]The resulting actual temperature is recorded.

[0016]Starting with a mix ratio between air and fuel set at random or last
set, the quantity of fuel supplied per unit of time with a constant
quantity of air supplied per unit of time is changed continuously or in
steps. By establishing and recording the temperature measured in the
effective region of the burner flame, the quantity of fuel supplied per
unit of time is set such that the measured temperature reaches a maximum.
The quantity of air supplied per unit of time is then increased by the
factor λhy, maintaining the previously set quantity of fuel
using the air mass flow sensor. In this way, for any desired burner load
with different gas qualities, but also by changing settings and by
changing the characteristics of the sensors disposed on the gas burner,
the desired value of the air ratio for hygienically optimal combustion is
set accurately, safely and reliably.

[0017]For reasons relating to the design, it can be possible for the
increase in air quantity to be inevitably also associated with an
increase in the quantity of gas. In this case, a mix geometry formed with
a suitable design can reduce the increase in the quantity of gas to a
negligible value.

[0018]However, by using mass flow sensors in the gas mass flow, a control
device without any structural adaptation can re-set the gas mass flow to
the value m.sub.GTmax found with Tmax by appropriately manipulating
the gas valve.

[0019]Finally, it is also possible to establish the increased gas mass
flow by calculation and to set the air ratio λhy
correspondingly higher. It can then also be considered to reduce the
quantity of gas by the calculated value, but this requires a very precise
valve.

[0020]In particular when there are fluctuations in the quality of the
combustion gas readjustment of the air ratio should be undertaken in
order to guarantee hygienically optimal combustion. Re-adjustment of the
air ratio can be implemented here, for example, at periodic intervals of
time, when there is a load change, when operation is started or when the
equipment is being serviced.

[0021]The firing device according to the invention, in particular a gas
burner, is adapted for implementing one of the methods specified above.

[0022]In particular, the firing device has a temperature sensor in the
effective region of the burner flame of the firing device. This
temperature sensor can be disposed in the core of the flame, at the foot
of the flame, at the top of the flame, but also some distance away from
the flame, for example on the burner plate itself.

[0023]Moreover, the firing device preferably has a gas valve with a
correcting element, in particular with a stepper motor, a pulse width
modulated coil or with a coil controlled by an electric value. Because
the method is particularly suitable for the electronic combination, the
aforementioned valves, which can be actuated simply and with precision,
can be used.

[0024]Furthermore, the firing device has a mass flow sensor and/or volume
flow sensor for measuring the quantity of air supplied to the firing
device per unit of time.

[0025]Further features and advantages of the object of the invention will
become evident from the following description of particular examples of
embodiments of the invention.

[0026]These show as follows:

[0027]FIG. 1 a firing device according to the invention;

[0028]FIG. 2 a characteristic for clarifying the method according to the
invention;

[0029]FIG. 3 a further characteristic for clarifying the method according
to the invention.

[0030]FIG. 1 shows a gas burner with which a mixture of air L and gas G is
pre-mixed and combusted.

[0031]The gas burner has an air supply section 1 by means of which
combustion air L is sucked in from a fan 9 with controllable speed. A
mass flow sensor 2 measures the mass flow of the air L sucked in. The
mass flow sensor 2 is disposed such that the most laminar flow possible
is produced around it so as to avoid measurement errors. In particular,
the mass flow sensor could be disposed in a bypass (not shown) and using
a flow rectifier. With the help of the mass flow sensor and the fan 9
with controllable speed, the supply of air into the mixing region 8 can
be precisely controlled.

[0032]For the supply of gas, a gas supply section 4 is provided which is
attached to a gas supply line. The gas supply section can be provided
with a mass flow sensor of a suitable design. By means of a valve 6, for
example a pulse width modulated or electronically controlled valve which
e.g. is equipped with a control element with a stepper motor, the flow of
gas through a line 7 into the mixing region 8 is controlled. In the
mixing region 8 mixing of the gas G with the air L takes place. The fan 9
ventilator is driven with an adjustable speed so as to suck in both the
air L and the gas G.

[0033]With a pre-determined air mass flow the valve 6 is opened
sufficiently far such that the air/gas mixture passes with the desired
mix ratio into the mixing region 8. The air ratio λ is set here
such that hygienically optimal combustion takes place.

[0034]The air/gas mix flows via a line 10 from the fan 9 to the burner
part 11. Here, it passes out and feeds the burner flame 13 which is to
emit a pre-determined heat output.

[0035]A temperature sensor 12, for example a thermoelement, is disposed on
the burner part 11. With the help of this thermoelement an actual
temperature is measured which is used when implementing the method
described below for setting the desired value Ah of the air ratio. In
this example, the temperature sensor 12 is disposed on a surface of the
burner part 11. It is also conceivable, however, to dispose the sensor at
another point in the effective region of the flame 13. The reference
temperature of the thermal element is measured at a point outside of the
effective region of the flame 13, for example in the air supply line 1.

[0036]A device (not shown) for controlling and regulating the air and/or
gas flow receives input data from the temperature sensor 12 and from the
mass flow sensor 2, and emits control signals to the valve 6 and to the
fan 9 drive. The opening of the valve 6 and the speed of the fan 9
ventilator are set such that the desired supply of air and gas is
provided.

[0037]Control takes place by implementing the method described below. In
particular, the control device has a storage unit for storing
characteristics and desired values, as well as a corresponding data
processing unit which is set up to implement the method.

[0038]The method according to the invention is described by means of the
characteristic shown in FIG. 2. In this figure the measured temperature
is shown dependent upon the air ratio λ.

[0039]At the start of the process, by means of the speed of the fan and
the opening of the gas valve, a specific air ratio λ0 is set
which corresponds, for example, to the last value set. In this case
λ0 lies above the value λ1 at which the temperature
maximum Tmax is given. By increasing the mass flow of burnable gas
supplied with a constant air mass flow mL1, λ is reduced. The
change to the gas mass flow can be implemented here for example in steps,
varying the steps of the stepper motor of the gas valve. With each step,
the actual temperature Tactual is determined by the temperature
sensor 12 which is disposed in the region of the burner flame. Using a
suitable iteration method, the opening of the gas valve is varied until
the temperature maximum Tmax is set.

[0040]In the second method step, the air mass flow mL1 is increased
by the desired value λhy of the air ratio, maintaining the
opening of the gas valve. The new air mass flow mhy=λhy
mL1 results. The air ratio is thus set exactly to the required
desired value λhy, and combustion takes place in a
hygienically optimal manner. After setting the desired air ratio
λhy the corresponding temperature Tdesired is measured.

[0041]With a load change, i.e. with a necessary change to the burner load,
the method is generally implemented again. The method can also be
implemented after switching on the gas burner or be repeated at
periodical intervals of time. In this way it is ensured that the gas
burner is constantly operated within an optimal range.

[0042]In order to prevent the method from having to be re-implemented with
each load change, a second characteristic line, as shown in FIG. 3, can
be established. In FIG. 3, the desired temperature Tdesired, which
was established as described in FIG. 2, is shown, dependent upon the air
mass flow mL1 which is directly in proportion to the burner load.
The desired value of the air ratio λhy is set precisely with a
specific burner load if the temperature Tactual measured in the
effective region of the burner flame corresponds to the desired
temperature Tdesired read out from FIG. 3. Regulation of the actual
temperature Tactual to the pre-determined desired value
Tdesired automatically leads to setting of the optimal air ratio
with a pre-determined burner load.

[0043]By using the characteristic shown in FIG. 3, over a specific period
of time over which the basic conditions do not crucially change, the
equipment can be operated without reimplementation of the method with
changing burner loads, i.e. in different operating states. However, the
characteristic should also be re-determined here at intervals of time or
at specific occasions, for example when servicing the equipment in order
to achieve adaptation to the gas quality made available or to
instabilities in the system.

[0044]In FIG. 3, the desired temperature Tdesired dependent upon the
mass flow of air mL, which corresponds to a specific burner load, is
shown. If the load is changed from an operating state 1 to an operating
state 2, according to the air mass flows mL1 and mL2, the
temperature of the gas burner is regulated so that the temperature
Tdesired2 is set. Moreover, the air/gas mix is thinned or enriched
by adjusting the gas valve 6.

[0045]Instead of totally re-determining the second characteristic
according to FIG. 3, if so required, individual values with specific
outputs can also be recorded and replace the values previously included
in the characteristic. It is also conceivable to shift the characteristic
overall according to a currently measured value with a specific load.

[0046]Implementation of the method leads to an operating mode with which
hygienically optimal combustion is achieved.